½ tablespoon French mustard, tarragon mustard or (for the adventurous) hot English mustard

3 tablespoons of flour

3 cups of full cream milk

50mls double cream

100 grams butter

¼ teaspoon of salt

pepper to taste

parsley, dill, chives, tarragon and/or thyme to taste

Pre-heat oven to 200°C

Add prawns and lobster shells to a small saucepan with a bay leaf, thyme and salt, add white wine and 1/2 cup of hot water and bring to a fast boil over a high heat.Boil vigorously for 15 minutes until a dark stock forms. Sieve liquor and set aside to cool .

In a large saucepan, sauté onion and celery with garlic in olive oil with a little of the butter until onion is soft - do not allow to colour.Once onion is translucent, add remaining butter and reduce heat.Once butter foams gently, add flour all at once and stir vigorously to incorporate.Warm through well to cook off raw flour taste before gradually adding prepared shellfish stock, milk and creamto form a thick sauce.Reduce heat and add seafood, stirring through carefully over a low heat until all ingredients are just coated with the sauce.

Transfer to an oven-proof dish.Layer over potatoes completely covering the seafood mix and sprinkle with herbs and gruyere cheese.Bake for 30 minutes or until cheese is golden brown and potatoes are cooked well with crispy brown edges.

Serve with fresh steamed asparagus, a light salad or just crusty bread!